The present invention relates to a sensor equipped with a trimming circuit which is applicable to a pressure sensor, an acceleration sensor, and other physical quantity sensors.
To downsize physical quantity sensors and reduce their manufacturing costs, it is preferable that the sensor has a smaller number of terminals used for the trimming adjustment of the physical quantity sensor. For example, the Japanese patent application Laid-open No. 11-30530(1999) corresponding to U.S. Pat. No. 6,324,482 (hereinafter, referred to as prior art document 1) discloses a sensor having an adjustment function. This sensor is arranged to operate in an adjustment mode when it receives serial transmission of an adjustment signal sent from an external signal source to its signal output terminal. This sensor requires no terminal dedicated to input of the adjustment mode signal. Furthermore, the Japanese patent application Laid-open No. 2002-350256 corresponding to U.S. Pat. No. 6,718,275 (hereinafter, referred to as prior art document 2) discloses a trimming circuit which is arranged to input a control signal to a logic circuit, has a trimming adjustment terminal provided to apply a writing signal of high voltage for writing data into a memory, and produces a signal for the trimming operation based on only the TRIM signal entered from this trimming adjustment terminal.
According to the sensor disclosed in the above-described prior art document 1, a microcomputer checks the value given via the signal output terminal from the outside at predetermined intervals, starts data reception of 1 byte in response to detection of a start bit and judges it as an erratic data when a stop bit is not correct. However, according to this arrangement, the microcomputer may frequently start data receiving actions in response to various signals, including external noise, entered into the signal output line. The processing burden of the microcomputer will increase. Furthermore, the trimming circuit disclosed in the above-described prior art document 2 requires a special terminal dedicated to the trimming adjustment and accordingly reduction in size and cost will be difficult.